group 2 elements(alkali earth metals)

• Key properties


  -Solid at room temp

  -Metallic bonding
• General trend of IE

  -Ionisation energy decreases as you go down Group 2:

  -atoms get bigger

  -more shielding

  -therefore weaker attraction from nucleus to electrons in outer shell
• General trend of mp

  -MP:Decreases.Increased distance between delocalised electrons and nucleus(metal ions get bigger)This means the attraction between the delocalised electron and nucleus gets weaker,therefore metallic bond gets weaker.
• Atomic radius,shielding,nuclear charge trends

  -Atomic radius+ionic radius decrease down group 2 -more electron shells so bigger atoms

  -Shielding increases down group-1 extra fully-occupied electron shell added before outer shell.This extra shell of electrons shield outer electrons more.

  -Nuclear charge increases down group-more protons.
• Extraction


  process of separating the metal from its ore.
• stages titanium is extracted by its ore


  1)Titanium dioxide heated with carbon and chlorine,to form titanium chloride TiO2+2Cl2+2C→TiCl4+2CO

  2)Then,the titanium is reduced by magnesium which forms magnesium chloride →TiCl4 +2Mg→Ti +2MgCl2
• Why isn't carbon used to extract titanium?

  Heating titanium dioxide with carbon produces a carbide which is too brittle to be useful as an engineering material.

  TiO2(s)+C(s)→TiC(s) +O2(g)
• use of calcium-calcium compound to prevent acid rain

  -Burning fossil fuels form so2,which causes acid rain

  -Two alternatives to spray over so2 instead:quicklime and limestone.
• quicklime to prevent acid rain

  -quicklime is mixed with water to form slurry(mixture) and is sprayed over so2 to form calcium sulfite solid

  CaO(s)+SO2(g)→CaSO3(s)
• limestone to prevent acid rain-


  -same process as quicklime but with calcium carbonate

  CaCO3(s)+SO2(g)→CaSO3(s)+CO2(g)
• group 2 reactivity with water

  -Reactivity increases down group-more vigorous.This is becase sum of sum of 2nd IE decreases therefore the activation energy to form s metal hydroxide decreases.
• the reactions with water:

  -beryllium doesn't react with water at room temp

  -magnesium with steam(alternative)

  Mg(s)+H2O(l)→MgO(s) +H2(g)

  -magnesium with cold water:reacts very slowly

  Mg(s) +2H2O(g)→Mg(OH)2(s)+H2(g)
• solubility rules

  -hydroxides solubility increase down the group

  -sulfates solubility decrease down the group

  -Barium sulfate insoluble,

  -caclium hydroxide and calcium sulfate sparingly soluble.
• compounds to remember

  slaked slime and lime water-Ca(OH)2
• uses of Mg(OH)2

  treats indigestion by neutralising stomach acid.
• uses of Ca(OH)2 (slaked lime)

  used to neutralise acidic soils and to encourage growth of plants.
• use of BaSO4 (barium meal)

  -used to diagnose stomach problems.It coats the tissue then shows up on x-rays-this is safe because barium sulfate is insoluable and won't dissolve in the body to cause harm.
• use of MgSO4

  epsom salt-a mineral used to replace magnesium in the body to increase water in the intestines.
• Using BaCl2 to test for sulfates

  -If barium ions are present in a solution then barium sulfate will form.

  -to form barium sulfate,the solution needs to be acidified e.g. eith hcl to remove any carbonate ions(which also show white precipitate).Positive test for BaSO4 result is a white precipitate
• State why H2SO4 shouldn't be used to acidify BaCl2

  H2SO4 contains sulfate ions which will react with BaCl2 to give a false positive result.
• Suggest why Magnesium Chloride wouldn't be a suitable test for sulfate ions

  MgCl2 will react with sulfate ions to form magnesium sulphate .However Group 2 solubility decreases down the group therefore magnesium sulpate is soluble and won't form a precipitate for a positive test result.
• oxidation of group 2 metals

  -they lose electrons when reacting e.g. metal - metal 2+ charge +2e-

  reaction is :metal → metal 2+ (charge) +2e-
• sodium oxide,aluminium oxide,MgO structure,bonding and mp

  Ionic lattice structure.Ionic bonding.Strong electrostatic forces of attraction=high mp. Al₂O₃ has some covalent character.
• SiO₂

  Giant covalent structure.Lots of strong covalent bonds=high mp
• P₄O₁₀

  -Simple covalent structure(covalent bonding).More electrons=stronger van der waals forces-this is what mp depends on.
• SO₂,SO₃

  Simple molecular.(same reasoning as phosphorus oxide).sulfur trioxide is higher mp than sulfur dioxide as it has more electrons.
• when comparing mp between simple molecular check which has more electrons
• Which oxides don't react with water

  Al₂O₃ SiO₂

  -SiO₂ has a giant covalent structure which prevents it from dissolving in water or reacting with water(water can't break down its structure).It only reacts with concentrated NaOH
• sodium oxide reaction with water and PH

  Na₂O(s)+H₂O(l)→2Na+ (aq)+2OH-

  PH=13-14
• Magnesium oxide reaction with water and PH

  MgO(s)+H₂O(l)→Mg(OH)₂(s)

  PH=9
• which oxides react with acids and which with bases?

  -oxides sodium to aluminium react with acids(aluminium oxide reacts w both)

  -oxides aluminium to sulfur trioxide react with bases
• P₄O₁₀ reaction w water,PH

  P₄O₁₀ +6H₂O(l)→4H₃PO₄(aq)

  PH=1-2
• P₄O₁₀ acid produced after reaction w water and structure

  PO₄3- (acid) ,tetrahderal structure